from the looks of it, each ticket costs $ 12...and there is a fixed rate of 150
ur equation would be : y = 12x + 150....where x is the number of students and y is the total cost...but that is an equation, and u want an expression...so I guess the expression would be 12x + 150
the cost of each ticket (12) multiplied by the number of students (x), added to 150 will give u the total cost